1. Field of Invention
This invention generally relates to reclamation of precious metals from circuit board scrap. More specifically this invention relates to dramatic improvements to the state of the art reclamation methods resulting from the breakthrough discovery that much more benign chemicals can be used for separation of unwanted metals, leaving only desired metal, when combined wanted and unwanted scrap metals are immersed in chemical baths that are subjected to an electromagnetic field at specific frequencies and power levels during processing.
2. Prior Art
The prior art discloses several different processes for recovery of precious metals from circuit board scrap all of which require a multitude of processing steps and equipment.
The first commonly used process is a complex dry process which involves pulverizing, crushing metals-containing scrap circuit boards into a fine powder, magnetic separation, electrostatic separation, air table separation and gravimetric separation. These processes are time consuming, capital intensive, require large machines, lots of floor space, dust collection systems, are labor intensive and only prepare the metal alloyed powders for further wet chemical and/or electrolytic separation. These processes are disclosed in Drage (U.S. Pat. No. 3,885,744), Drage (U.S. Pat. No. 3,905,556), Alavi (U.S. Pat. No. 5,139,203), Feldman (U.S. Pat. No. 5,217,171), Izumikawa (U.S. Pat. No. 5,630,554), Yokoyama (U.S. Pat. No. 5,676,318), and Chapman (U.S. Pat. No. 5,887,805).
The second major process for precious metals reclamation from printed circuit boards involves a process where the circuit boards are pyrolized in a closed loop system consisting of a scrubber, bag house and incinerator. Theses processes are disclosed in Bickford (U.S. Pat. No. 5,662,579), Wicks (U.S. Pat. No. 5,843,287), Chang (U.S. Pat. No. 5,979,033), and Wicks (U.S. Pat. No. 6,143,139). The incinerated product is then placed into a crucible furnace with the proper fluxing agents and reduced to metal and cast into unrefined bars. The unrefined bars are then placed into a blast furnace to remove all deleterious components and subjected to further refining steps such as processing requiring wet chemicals and/or electrolysis for final separation.
The wet chemical stripping processes utilize strong hydrochloric, sulphuric and nitric acids and a caustic soda solution and/or electrolytic processes involving casting the alloyed metals into anodes and placing them in galvanic baths depending on the particular metal being reduced or stripped. All the above drawbacks are involved in this process plus an additional hazard to control of the dibenzo-p-dioxins and dibenzo-furans given off when the scrap is incinerated with a halogen flame. This can be a four month long process with many processing steps.
Behr Precious Metals, Inc. discloses in a conference paper presented at NEPCON West—1994 entitled Refining and smelting of precious metals from printed circuit boards the third process, involving wet chemistry processes which subject surface plated boards and or parts to a cyanide stripping action in an agitated tumbler that allows the precious metals to be placed in solution, reclaimed from solution, refined and melted into bars. Environmental concerns may rule out this process in the future.
All of the above processes suffer from the following disadvantages:
(a) They all, with the exception of the cyanide stripping of surface plating, begin with the associated non-metal boards crushed into powder along with the metals or pyrolized with associated separation problems, expense and hazards.
(b) Once the metal fractions have been separated out from the non-metals then a slow wet chemistry and/or electrolytic process is required with multiple steps and baths utilizing very strong acids and bases to separate the various metals, casting into anodes and subjecting the anodes to galvanic baths for final refinement.
(c) All these methods are capital and labor intensive.
(d) They all require significant floor space and energy consumption.
(e) They all require significant safeguards as to dust collection and waste chemical disposal.